Many spatial light modulators (SLMs), such as the digital micro-mirror device (DMD™) are inherently progressive display devices. Therefore, systems built around these devices require scan-rate conversion of their interlaced video signals in order to double the vertical resolution of each image field. FIG. 1a illustrates an interlaced frame 100, which consists of two fields, field A 101 (dotted line) and field B 102 (solid line). For example, in an NTSC signal these field are approximately 16.7 mSec apart in time with the lines from field A 101 being presented on the TV screen and then the lines from field B 102 being inserted between the field A lines, so that two 60 Hz fields are combined to provide a 30 Hz interlaced frame rate. However, in a progressive display system 150, every line 151 is displayed in every field 150, as shown in FIG. 1b, thereby doubling the vertical resolution of the display.
To produce the sharpest image, these scan rate converters need to be content dependent. In other words, the scan rate converter must analyze the motion patterns of an interlaced image sequence and determine the most suitable method for scan rate conversion, on a pixel-by-pixel basis.
If the interlaced image sequence is created from a progressive source, such as film, having been broken apart into two fields for television presentation, then the scan rate converter can combine adjacent interlaced fields to form the original progressive frame. By performing this film mode detection and correctly jamming adjacent fields, the highest amount of detail is produced in the resulting image.
However, when the original source is an inherently interlaced signal, then the scan rate converter must determine how best to combine information from the current interlaced field and the previous interlaced field. In the absence of motion, the current field and the previous field may be jammed together to form a progressive image with the highest amount of detail. But, if motion is detected, information from the previous interlaced field cannot be used. A moving object is not in the same spatial location in 2 adjacent fields. Therefore, a field jam would produce a progressive image with 2 copies of the moving object. Hence, pixel values must be interpolated from the current field when motion is detected. In order to minimize the loss of vertical detail in moving objects, the scan rate converter must perform interpolation along edges.
In addition, noise on the video must be considered in the scan conversion process since it can give a false indication of motion and can also blur the high spatial detail of the image.
In general, in conventional de-interlacing techniques, the vertical resolution of the new progressive image is accomplished by jamming the odd and even field lines, but only when there is no motion. When there is motion, then only the current field is used and the lines above and below the current pixel are averaged.
What is needed is a highly integrated scan rate converter that determines, on a pixel-by-pixel basis, if motion is present in the image and then determines the best value for each pixel for a high resolution progressive image. This method needs to interpolate along edges, rather than across them. This solution further needs to include adaptive noise reduction, also on a pixel-by-pixel basis, to prevent false motion detection and assure high spatial detail in the image. The features incorporated in the method and implementation of the present invention meets these needs.